Solenoid proportional control valves for flow rate control have long been used to control the flow rate of liquid fuels and other fluids in various systems. Consider, for example, the fuel injection system that accumulates high-pressure fuel in a common rail and injects the high-pressure fuel through injectors into the cylinders of an internal combustion engine. The pump unit provided for feeding the high-pressure fuel into the common rail in this system includes a feed pump for feeding fuel from a fuel tank and is configured to pressurize the fuel supplied by the feed pump using a high-pressure plunger and to feed the highly pressurized fuel into the common rail. The fuel supplied from the feed pump to the high-pressure plunger is controlled to an amount appropriate for the instantaneous operating condition of the engine by a solenoid proportional control valve.
The solenoid proportional control valve used for this purpose is equipped with a spring-biased piston slidably accommodated in a cylinder and a solenoid for positioning the piston against the biasing force of the spring. The positional relationship between the piston and cylinder is controlled in proportion to the magnitude of the driving current supplied to the solenoid to regulate the open area of a fuel passage port formed in the cylinder and thus regulate the flow rate of fuel passing through the solenoid proportional control valve.
Ordinarily, the coil of the solenoid of the so-configured solenoid proportional control valve is supplied with a constant frequency pulse voltage and the fuel flow rate is regulated by varying the duty ratio of the pulse voltage so as to regulate the effective value of the driving current supplied to the solenoid.
In the so-configured solenoid proportional control valve, however, static and dynamic friction arises between the piston and cylinder during operation, and the hysteresis produced in the movement of the piston by this mechanical operating friction causes a decline in the responsivity of the valve system, deviation in the controlled flow rate and other effects that create a problem by making it impossible to conduct the flow rate control stably.
An object of the present invention is to provide a method and apparatus for driving a solenoid proportional control valve utilized for flow rate control that can overcome the aforesaid problem of the prior art.
Another object of the present invention is to provide a method and apparatus for driving a solenoid proportional control valve utilized for flow rate control that can realize stable flow rate control.
Another object of the present invention is to provide a method and apparatus for driving a solenoid proportional control valve utilized for flow rate control that can realize stable flow rate control without increasing cost or electric power consumption.